Piston and cylinder construction



March 25, 1947. H. F. SCHMIDT PISTON AND CYLINDER CONSTRUCTION FiledApril 26,' 1945 Patented Mears," 1941 A sV PATENT omer-:f

Hs'roN AND oYuNpEn CONSTRUCTION Howard F.u Schmidt, San Diego,

Calif., assigner to Consolidated Vultee Aircraft Corporation,

. San Diego, Calif.

' Appiicauqn April 2s, 1945, serial No. 590,331

(c1. soa-f4) 4 Claims.

The invention relates to hydraulic devices for actuating elementsbetween alternate positions such, for example,- as airplane controlmechanisms.

In hydraulic devices or jacks used for actuating mechanisms,particularly in aircraft, which comprise a piston operable by uid underpresportions oithe piston strokes for efficient operation and withoutloss of fluid pressure.

sure in opposite directions in a cylinder, it is del fsirable toprevent-thev loss of operating pressure at the ends of thepiston-strokes `for maintaining maximum eiciency in holding the devicein its alternative positions. When the piston i's equipped with packingrings of the iixed compressiontype, they cause excessive `frictionbetween the piston and cylinder-wall during the entire piston strokeswhich results in retardation in the operation of the pistons. Inpractice, it has been found that loss of fluid pressure by i leakagearound the piston occurs mainly at the ends of the strokes of the pistonwhen the actuated device has completed its cycle of operation and isretained in one of its alternative positions by the huid pressureagainst the piston. It has also been found that rings, which aresubjected to wedging expansion during the entire piston strokes, produceobjectionable retardation to the operation of the actuated device by thepiston. This object is attained primarily by providing a pistoncomprising relatively movablesections on a stem which is.connected tothe device to be actuated and an elastic packing-ring, the ring andring-engaging portions of the piston-sections having cross-sectionalcontours, for example, circular and rectangular, whereby the ring willbe 2 deformed to apply friction of low magnitude to the cylinder betweenthe ends of the piston strokes and will be deformed so its outer portionwill be expanded outwardly to produce a vgreater A degree of friction onthe cylinder at the ends of the piston strokes.

One .object .of the invention is to provide improved packing or sealingmeans between the pis- -ton and the cylinder which produces relativelylow frictionbetween them and less resistance to the movement of thepiston during travel of the piston between the ends of its strokes and asubstantially greater friction between the plstons and cylinders at` theends of the pistonv strokes while the element actuated bythe pistonV ishydraulically retained in one of its alternative' positions. l 3

Another object of the invention is to provide a hydraulic device inwhich the piston isequipped with a packing ring or rings which producedifferential friction at the ends and intermediate under pressure in theopposite ends of Other objects of the invention will appear from thedetailed description.

The invention 1consists in the several featuresl hereinafter `set forthand more particularly deiined by claims at the conclusion hereof.

In the drawings:

Fig. 1 isv a longitudinal section o1' hydraulic Jack, the piston beingshown in elevation.

Fig. 2 is a longitudinal section on a larger scale illustrating thepiston during an intermediate portion of its stroke.`

Fig. 3 is a similar view illustrating the piston at the end of itsstroke.

The invention is exempliiied in a hydraulic jack which comprises acylinder I@ which'is provided at one end with a head il' and at itsother end with ahead I2. Pipes 25, 2t are connected to the cylinderadjacent its opposite ends for alternately .admitting iiuid underpressure and simultaneously exhausting fluid from the opposite ends ofthe cylinder. A piston is .slidable in the cylinder and is carried by astem i5 which extends through head i2 for connection to a device to beactuated such, for example, as a control device on an airplane. Suchconnections are well understood in the'art and are usually operable toshift the actuated element betweentwo alternative positions in whichthey are held by the iiuid the cylinder, respectively. l f

The piston comprises a pair of disk-like secn tions Il, 18 which have alimited sliding movement on a reduced portion 2t of the stem i5 betweena shoulder 2i on the stemand a nut 22 which is screw-threaded to the endof stem l5 and seated on a shoulder 23. The piston-sections il, I8 areslidable on the stem i5 and relatively to each other. Pistoni-section ilis provided on its inner side adjacent its periphery with an annularface 23. Piston-section i8 is provided adjacent its periphery with anannular groove hav-l ing an inner cylindrical side or peripheral face 30which is parallel to the axis of the pistonstem i5 and a side-face 3lwhich is parallel to face 28. Faces 30, 3| in cross-section extend atright angles to each other. Inwardly of face 30, a recess 33 is formedin the inner face of piston-section il, and piston-section i8 is formedwith a face 34 which is adaptedto .extend into recess 33. The grooveforming-faces 30, 3| on piston-section I8 and the face 28 onpiston-section I1 form in eiect a groove which is rectangular incross-section with parallel sides. An elastic left in the graove intowhich the ring can be distorted by pressure applied to the ring by thepiston-sections I1, i8 before its outer portion is expanded tosubstantially increase its pressure against the cylinder. The elasticring '35 has a suflicient density or co-etiicient of elasticity toretain approximately its circular cross-sectional.

contour or be deformed into the space in the groove during theapplication of the normal load inder to the other.

vpressure exerted against piston-section I1 will deform the elastic ring35 so it will ll the groove in piston-section I8 and between saidpistonsections, and expand the outerportion of said ring firmly againstthe inner periphery of the cylinder I to substantially lock the pistonin the cylinder by said friction. During the same cycle of movement.ring 40 will operate in like manner and prevent leakage between thepiston-stem I and the piston-section from one end of the cyl- Thepressure is usually retained in the cylinder to hold the actuatedelement in one of its alternative positions, and the action of thepacking-rings above-described will maintain an eiective seal between thepiston and cylinder and the piston and its stem. When the element is tobe actuated in the opposite direcso that the friction or pressure of thering on the cylinder will be sufficient to prevent the flow of fluidfrom one side of the piston to the other without substantial increase offriction against the cylinder or retardation to the movement of thepiston in the cylinder between the ends of the piston strokes. When theload on the piston is increased at the end of its strokes, which occurswhen the actuated element has been shiftedl to one of its alternativepositions, the increased pressure on the piston will deform the ring toli the groove in which it is held and also expand its outer portion toexert a substantially greater pressure against the cylinder. Thisincreased pressure of the elastic ring against the cylinder willpositively prevent any leakage around the piston and the ring will bemaintained expanded while the piston remains held by fluid underpressure at the end of its strokes. A similar diilerentiaily actingpacking is provided between the piston-sections I1, I8 and thepistonstem I5. Piston-section I8 is provided around the piston-stem I 5with an annular groove which is right angle in cross-section andincludes av straight side face 31 and a cylindrical periphery 38, andpiston-section I1 is provided with an annular face 39 which issubstantially parallel to the face 31. These faces with the piston-stemI5 form a substantially rectangular groove in which an elastic ring MIis conned. Ring 40 is normally circular in cross-section and is ofsufficient density to retain approximately its normal cross-sectionalshape during the normal loading ofthe piston between the ends of itsstrokes. At the end of the piston strokes, the increased load will forcethe piston-sections I1, I8 together suinciently to deform the ring 40 toll said rectangular groove so that the portion which engages thepiston-stem I5 will be forced with greater pressure against the stem andprevent leakage through the piston. Y

In the operation of the piston in one direction by fluid under pressureentering the cylinder I0 throughpipe 25 and simultaneously exhausting itfrom the other end of the cylinder through pipe 26, the normal load onthe piston will be such that its pressure against piston-section I1 willengage packing rings 35 and 40 without sumcient deformation of saidrings between piston-sections I1, I8. to substantially increase thefriction between packing-ring 35 and the cylinder I0, and betweenpacking-.ring 4I) and the piston-stem I5. The low degree of friction'between cylinder I0 and ring 35 results in low retardation to themovement of the piston. As the piston reaches the .end of its leftwardstroke, the load on the piston-stem I5 willfbe greatly increased by thestoppage of the actuated device. The increased tion, fluid underpressure will be admitted to the cylinder through pipe 26, andsimultaneously exhausted through pipe 25. Between the ends of therightward stroke, the piston-rings 35, 40 will operate as beforedescribed to exert a low degree of friction between the piston and thecylinder and between the piston and its stem. When the piston reachestheend of its rightward stroke, the increased load on the piston willcause rings 35, 40 to be deformed to fill the grooves in which they areconfined, so the pressure of ring 35 against the cylinder and thepressure of ring 40 against the piston-stem will be increased in thesame manner before described.

The invention exemplifies a hydraulic actuating device including apiston and a cylinder operable in opposite directions by fluid underpressure in which the piston is formed of sections, and an elasticpacking-ring is operative to exert relatively slight friction againstthe cylinder during the normal operating load between the ends of thepiston strokes, and to exert substantial locking engagement between thepiston and the cylinder. while fluid remains under pressure in one endof the cylinder, and a similarly operative elastic packing-.ring betweenthe piston-sections and the .piston-stem.

may be extended through the other end or through both ends of thecylinder.

The invention is not to be understood as limited to the detailsdescribed, since these may be modified within the scope of the appendedclaims without departing from the spirit and scope of the invention.

Having thus described the invention, what I claim as new and desire tosecure by Letters Patent is: c

1. The combination with a cylinder provided with connections for iiuidto and from its opposite ends, of a piston slidable in oppositedirections in the cylinder by fluid under pressure alternately deliveredto the opposite ends of the cylinder, comprising, a piston-stemextending through one end of the cylinder for connection to a device tobe actuated, a pair of piston-sections slidably mounted on the stem forlimited movement thereon andrelatively to each other, having confrontingfaces provided with means forming peripheral normal load between theends of its strokes and being distortable by the sections tosubstantially fill the groove' and be expanded for a substantialincrease of friction between the ring and cylinder when the pistonreaches the ends of its strokes and is loaded against further movement.

2. The combination with a cylinder provided with connections for uid toand from its opposite ends, of a piston slidable in opposite directionsin the cylinder by fluid under pressure alternately delivered to theopposite ends of the cylinder and comprising a piston-stem extendingthrough one end ofthe cylinder for connection to a device to beactuated, and a pair of piston sections slidably mounted on the stem forlimited movement thereon and relatively to each other and having .facesforming a substantially parallelsided peripheral groove between them,andan elastic ring in said groove.- having a cross-sectional contourwhich normally leaves a space in the groove and around the ring, thering having sufiicient density to prevent substantial expansion by thesections when the piston is under normal load between the ends of itsstrokes and being distortable by the sides of the groove tosubstantially ll the groove and expansible f or a substantialincrease offriction between the ring and the cylinder when the piston reaches theends of its strokes and is loaded against further movement.

3. The combination with a. cylinder provided with connectionsfor fluidto and from its opposite ends, of a piston slidable in oppositedirections in the cylinder by uid under pressure alternately deliveredto the opposite ends of the cylinder and comprising a piston-stemextending through one end of the cylinder for connection to a device tobe actuated, and a. pair of piston sections slidably mounted on the stemfor limited movement thereon and relatively to each other and havingfaces forming a pair of substantially parallel-sided peripheral groovesbetween them. said grooves being disposed at the outer and innerperipheries of the piston, respectively, and elastic rings in thegrooves, respectively, each being of substantially circularcross-sectional contour tially nil them and being expansible for asubstantial increase of friction between the 'rings and the cylinder andthe stem, respectively, when the piston reaches the ends of its strokesand is loaded against further movement.

4. The combination with a cylinder provided with connections for iiuidto and from its opposite ends, of a piston slidable in oppositedirections in the cylinder by fluid under pressure alterwhich leaves aspace in its groove and around tortable by the sides of the grooves tosubstannately delivered to the opposite ends of the cylinder andcomprising a piston-stem extending through one end of the cylinder forconnection to a device to be actuated, and a pair-of piston sectionsslidably mounted on the stem for limited movement thereon and relativelyto each other and having faces forming between them a. peripheral groovewith substantially parallel sides and a straight bottom, and an elasticring in said groove of substantially circular cross-sectional contourwhich normally leaves a space in the groove and around the ring, thering having sumcient density to prevent substantial expansion by thesections when the piston is under normal load between the ends of itsstrokes and being distortable by the sides of the groove tosubstantially fill the groove and being expansible for a substantialincrease of friction between the ring and the cylinder when the pistonreaches the ends oi' its strokes and is loaded against further movement.

HOWARD F. SCHMIDT.

REFERENCES CITED The following references are oi' record in the ille ofthis patent:

UNITED s'rA'rEs PATENTS

